The invention relates to a power steering device for a motor vehicle.
Power steering systems are generally known and are commonly used in motor vehicles. In these systems a power steering pump circulates hydraulic fluid which is used for assistance in the execution of steering movements. Power steering pumps driven by an internal combustion engine circulate a specific quantity of oil constantly, however, even when this is not required. This consumes energy and generates heat and pollutants which have to be disposed of.
EP A1-1109638 discloses a power steering system with a regulated power steering pump in which the oil quantity is regulated as a function of the steering assistance requirement. The oil quantity is set by means of the opening ratio of the regulating valve in proportion to the electrical control current. However, in the event of a system failure, power assistance is no longer available.
U.S. Pat. No. 4,828,065 discloses a bypass valve which is arranged in a parallel branch to a power steering device and through which hydraulic fluid can bypass a steering valve.
It is the object of the present invention to provide a power steering device which still provides power assistance even in the event of a failure of the regulating valve.